1. Field of the Invention
The present invention relates to a laser diode formed by encapsulating a laser diode chip in a resin and, more particularly, to a technique for preventing the breakage of the resin on a light-emitting end face of the laser diode chip due to the emission of a laser beam.
2. Description of the Related Art
As shown in FIG. 6, a known laser diode chip is arranged such that an n-type clad layer 113 formed of aluminum-gallium-arsenide (AlGaAs), an active layer 114 formed of gallium-arsenide (GaAs), a p-type clad layer 115, and a p-type cap layer 116 are laminated on an n-type GaAs substrate 112. An electrode 117 is selectively formed on the obverse surface of the laser diode chip in an opening of the p-type cap layer 116, while a rear electrode 8 is formed on the reverse surface of the GaAs substrate 112, so as to form a laser diode chip 111 of a double heterostructure (DH structure). In addition, as shown in FIG. 7, this laser diode chip 111 is mounted on a radiation plate 23a, and the assembly is encapsulated with an encapsulating resin layer 9 formed of a transparent epoxy resin or the like. In FIG. 7, reference numeral 20a denotes a lead frame; numeral 21 denotes a gold wire used for the wiring of each electrode; and numeral 22 denotes a photodiode.
In the above-described conventional laser diode, problems arise because the epoxy resin directly abuts against a light-emitting end face 33, through which a laser beam is emitted from a light-emitting area 35 of the laser diode chip 111. If the laser diode is continuously oscillated, the encapsulating resin layer 9 in the vicinity of the light-emitting end face 33 is decomposed by the heat generated at this face. Since the decomposition of the resin layer 9 lowers the light emission efficiency of the laser diode, the amount of generated heat increases, causing promotion of the decomposition. In some cases, the promoted decomposition results in the formation of a cavity in the encapsulating resin layer 9 in the vicinity of the light-emitting end face 33.
For example, in a case where a laser diode with an output of 5 mW and an oscillation wavelength of 780 nm is continuously oscillated in a state close to its maximum rating, a conical broken area having a bottom diameter of 5 .mu.m and a height of 5 .mu.m is formed in the encapsulating resin layer 9 in the vicinity of the light-emitting end face 33 after a lapse of approximately 1000 hours.
Additionally, where a laser diode with a maximum rating of 5 mW is used as a pickup for an optical recording medium, and is continuously operated at an operating current of about 55 mA and at an ambient temperature of approximately 60.degree. C., the encapsulating resin layer 9 in the vicinity of the light-emitting end face 33 melts and breaks. As a result, a cavity is formed after approximately 40 to 60 hours of use by the optical energy of the laser beam, and the light waves of the laser beam are disturbed.